Resistive materials and method of making such materials

ABSTRACT

A resistive film composition consisting essentially of AlN and solid solution of TiN and ZrN and a method of making the same by means of a cathodic sputtering.

United States Patent [191 Wasa et al. I

[111 3,303,057 Apr. 9, 1974 RESISTIVE MATERIALS AND METHOD OF MAKING SUCH MATERIALS [75] Inventors: Kiyotaka Wasa, Nara; Fumio HO SQII Ii; Shigeru I-Iayakawa, both of Osaka, all of Japan [73] Assignee: Matsushita Electric Industrial, Co.

Ltd., Osaka, Japan [22} Filed: Feb. 17, 1972 [21] Appl. No: 227,070

[30] Foreign Application Priority Data Mar. 17, 1971 Japan 46-15273 Mar. 17, 1971 Japan Mar. 11, 1971 Japan.. 46-13829 [52] US. Cl 252/518, 117/221, 252/520,

a a v 7 218/ 15. [51] Int. C IIL'L II.I..I. ....H0lb 1/06 [58] Field of Search 252/518, 520; 117/221 [56] References Cited UNITED STATES PATENTS 3,011,983 12/1961 Ricker et al 252/520 3,394,087 7/1968 Huang ct al. 252/518 3,544,486 12/1970 Passmore 252/518 OTHER PUBLICATIONS Chernjcal Abstracts, Vol. 45, C01. 1414 d, Vol. 54,

C01. 8020 d. Bush et al., J. of Applied Physics, 20, 295-296 (1949).

Primary Examiner-John D. Welsh Attorney, Agent, or Firm-Wenderoth, Lind & Ponack 5 7] ABSTRACT A resistive film composition consisting essentially of AlN and solid solution of TiN and ZrN and a method of making the same by means of a cathodic sputtering.

2 Claims, 7 Drawing Figures RESISTIVITYVQJI cm,

AlN (MomPERcENT) PATENIEDMR 91914 3L803L05T sum 3 OF 5 RESISTIVITY 10 CM) O 20 4O 6O 80 J00 L0 Lu Q Q Tl -zr-AQ 0 Q: I 9 'CATHODE L I if N U lg COMPOSITION OF COMPOSITE CATHODE (AREA FRACTION OF Zr METAL,

FIG.3

RESISTIVE MATERIALS AND METHOD OF MAKING SUCH MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel resistive material for manufacturing thin film resistors and to a method of making such a material. More particularly, it relates to a resistive film composition consisting essentially of AIN and solid solution of TiN and ZrN and to a method of making this material by cathodic sputtering.

2. Description of the Prior Art Considerable effort has been devoted to developing highly resistive thin film resistors with good electrical stability. Thin films of refractory metals, alloys, nitrides silicides, oxides and metal-dielectric mixtures (cermets) have been evaluated for use in manufacturing the highly resistive thin film resistors. Among them, thin films of nitrides such as TaN and TiN having a high melting point have been felt to have practical importance in the manufacturing of the precise thin film resistors with good electrical stability. However, these nitride films according to the prior art have resistances in only ,a narrow range, such as from 100 to 300 pflcm in specific resistivities.

The present invention provides a novel resistive material consisting essentially of AIN and a solid solution of TiN and ZrN for the manufacturing of the precise thin film resistors having a wide range of resistivities and good electrical stability. Those skilled in the art will recognize that this novel material according to the present invention is indispensable to the manufacturing of precise thin film resistors having a wide range of resistivities.

SUMMARY OF THE INVENTION It is an object of the present invention to provide resistive materials having a novel composition for the manufacturing of precise thin film resistors having a wide range of resistivities and good electrical stability.

These objects are achieved by providing a resistor composition which is especially good for thin film resistors and having a composition consisting essentially of AIN and a solid solution of TiN and ZrN, the composition having a cermet type of structure. The material is made by electron beam deposition, ion beam deposition or cathodic sputtering on a suitable substrate.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1-5 are diagrams showing the resistive properties of the thin resistive films consisting essentially of AIN and a solid solution of TiN and ZrN for various concentrations of AlN, TiN and ZrN in accordance with the present invention; and

FIGS. 6 and 7 are diagrammatic view of the cathodic sputtering apparatus which is used in the method of making precise thin film resistors having a wide range of resistivities in accordance with the present inven tion.

DESCRIPTION OF THE PREFERRED EMBODIMENT The resistive materials for the manufacturing of precise thin film resistors having a wide range of resistivities according to the present invention consist essentially of AIN and a solid solution of TiN and ZrN. The structure of said resistive materials is similar to the cermets, wherein the metallic conductor is said solid solution of TiN and ZrN and the dielectric is said AIN.

Thin resistive films of said resistive materials according to the present invention can be made by suitable methods of depositing thin films, such as an electron beam deposition method, an ion beam deposition method or a cathodic sputtering method. For instance, said thin resistive films can be made on substrates of suitable material, such as alumina, glass or any other material having a low electrical conductivity by ion beam deposition from a composite target electrode consisting essentially of AIN, TiN and ZrN, and can also be made on said substrates by cathodic sputtering from a composite cathode consisting essentially of Al, Ti and Zr in a nitriding atmosphere.

It is preferable that the partial pressure of residual gases, including 0, 0 OH, H 0 and hydrocarbons, be kept below 1X10 Torr during deposition of said thin resistive films, and that said substrates be kept at an elevated temperature, such as to 300C during deposition of said thin resistive films. It is also preferable that said substrates be annealed after deposition of said thin resistive films in air for 5 to 10 hours at an elevated temperature, such as 250 to 300C. Keeping the residual gases at a low partial pressure inhibits the incorporation of oxides, such as Al O TiO, Ti0 or ZrO in said thin resistive films. Elevating said substrate temperature during deposition of said thin resistive films and during annealing of said substrate after deposition of said thin resistive films results in an increase in the stability of the resistive properties, of said thin resistive films according to the present invention.

FIGS. 1 and 2 show the resistive properties of said thin resistive films consisting essentially of AIN and a solid solution of TiN and ZrN for various concentrations of AlN, TiN and ZrN when the thin resistive films are made by said cathodic sputtering. The resistivity is denoted for films having thicknesses of 800 to 3,000 A. on glass substrates. The temperature coefficient of resistivity is determined from the average values between 20 to 80C. The concentrations of AIN, TiN and ZrN described are estimated by assuming that the amount of each component deposited will be proportional to a fraction of the area of the surface of said composite cathode which is of the metal of the component, and will also be proportional to the relative sputtering rate. These estimations are supported by electron micrographic analysis and the mass-spectropic analysis.

Referring to FIGS. 1 and 2, it is seen that the resistivity and the temperature coefficient of resistivity are 250 pflcm and ppm/C, respectively, for the TiN thin films. By introducing the AIN into the TiN, the resistivity of the resultant films consisting of the Ti-A- l-N system increases and the temperature coefficient decreases with increasing AlN concentration. At about 50 mole percent of AlN in the Ti-AlN system, the films have a zero temperature coefficient and a resistivity of 600 uflcm. At higher AlN concentrations in said TiAl-N system, the resistivity increases significantly. However, the temperature coefficient tends to a large negative value. For instance, at 70 mole percent of AlN, the resistivity is about 3,000 cm with a temperature coefficient of 1 ,000 ppm/C.

Referring again to FIGS. 1 and 2, it is seen that the films of Ti-ZrAlN system can provide higher resistivity with a smaller temperature coefficient of resistivity than films of the TiAl--N system. FIG. 3 is a diagram showing the resistive properties of the Ti-A- l-N system and the TiZrAl-N system, the amounts of material in the film resistor being proportional to the amounts of metal in the composite cathode used to form the film which is exposed on the surface of the electrode. Referring to FIG. 3, it is noteworthy that the TiAl-N system has a resistivity of only 1,000 item for a material with a temperature coefficient of 200 ppm/C, while the TiZrAl--N system can provide a resisitivity as high as 8,000 ptQcm for a material with the same temperature coefficient.

It has been discovered that a resistive film material consisting essentially of AlN and a solid solution of TiN and ZrN, wherein the concentration of AlN ranges from to 50 mole percent, the concentration of TiN ranges from 10 to 80 mole percent, the concentration of ZrN ranges from 10 to 90 mole percent, and the mole ratios of AlN to TiN, [AlN]/[TiN], are less than 1.2. can provide resistive films having a wide range of resistivities, such as from 350 to 10,000 uflcm, with temperature coefficients of 200 to +150 ppm/C.

It has also been discovered according to the present invention that a'resistive film material consisting essentially of AlN and a solid solution of TiN and ZrN, wherein the concentration of AlN ranges from 10 to 40 mole percent, the concentration of TiN ranges from 40 to 70 mole percent and the concentration of ZrN ranges from to 50mole percent, can provide resistive films with a very small temperature coefficient such as +125 to 125 ppm/.C with resistivities in a range of 350to 1,000 pflcm.

Table 1 summarizes the typical resistive properties of the resistive films according to the present invention.

' Table l Referring to Table 1, it is further noted that the resistivity of TiN filmscan be extended by one order or more by the introduction of ZrN and AlN.

The resistive films according to the present invention can be prepared by cathodic sputtering from a composite cathode consisting essentially of Ti, Zr and Al in a nitriding atmosphere as described hereinbefore. This causes the composite cathode materials to be nitrided so as to form mixed nitride films consisting essentially of MN and a solid solution of TiN and ZrN on a substrate.

FIGS. 4 and 5 show the variation in the resistive properties of said mixed nitride films with the composition of the composite cathode. In the figures, the composition denotes the area fraction of each component on the surface of said composite cathode.

It has been discovered that the resistive films having a wide range of resistivities, such as 350 to 10,000 uflcm, with temperature coefficients from 200 to :t150 ppm/C, and the composition of which consists essentially of 10 to 50 mole percent of AlN, 10 to mole percent of TiN, 10 to 90 mole percent of ZrN, and having mole ratios of AlN to TiN of less than 1.2, can be made from a composite cathode consisting essentially of Al, Ti and Zr and having a structure such that the surface area thereof is 5 to 40% Al, 15 to Ti, and 10 to Zr, and the ratio of the areas of Alto Ti being less than 0.7.

It has also been discovered that the resistive films having a very small temperature coefficient, Such as +125 to l25 ppm/C, and resistivitiesin the range of 50 to 1,000 uflcm, and having a composition which consists essentially of 10 to 40 mole percent of AlN, 40 to 70 mole percent of TiN and 20 to 5.0 mole percent of ZrN, can be made from a composite cathode consisting essentially of A1, Tiand Zr and having a composition such that the surface area is to 26% Al, 45 to 75% Ti, and 20 to 50% Zr.

It is preferable that the cathodic sputtering step be conducted at alow residual gas pressure by using a low pressure sputtering apparatus such as a magnetron type sputtering apparatus described in U.S. Pat. No. 3,528,902.

Referring to FIGS. 6 and 7, there is illustrated a magnetron type sputtering apparatus comprised of a pair of concentric cylindrical electrodes 2 and 3 mounted within a cylindrical envelope 4 having an inlet 5 and an outlet 6. Said electrodes 2 'and 3 are connected across a voltage supply source 7. Either of said cylindrical electrodes 2 and 3 can be the cathode, but it is preferred that said inner electrode 2 be the cathode. Substrates 8 to be coated are secured to the anode. The cylindrical envelope 4 contains an ionizable medium and can be made of anygas-tight, nonmagnetic material.

Said cylindrical envelope 4 containing said pair of electrodes is positioned in a magnetic field parallel to the sides of said cylindrical electrodes 2 and 3 so that said field is transverse to the discharge from said electrodes. Said field can be supplied by any available magnetic field creating means 9, such as an electro-magnet externally attached across the flat end surfaces of said cylindrical envelope 4.

The ionizable medium can be nitrogen gas or a mixture of nitrogen and argon gas at a pressure of 10" to 10 Torr. The cathode is a composite cathode of Al, Ti and Zr, as described hereinbefore. Said composite cathode can be prepared by using any available and suitable method. A preferred method is to press a mixture of Al, Ti and Zr metal in powder form, the powder having a particle size of to 300 mesh, at a pressure of 30,000 to 100,000 psi. Use of said magnetron type sputtering apparatus makes it possible to provide resistive films consisting essentially of AlN and a solid solution of TiN and ZrN, the resistive properties of which are as described in connection with FIGS. 1 and 2.

It has also been discovered that a low pressure sputtering apparatus such as r-f sputtering apparatus makes it possible to make thin resistive films consisting essentially of MN and a solid solution of TiN and ZrN by using a composite cathode under low residual gas pressure.

It has also been discovered that a composite cathode consisting essentially of to 50 mole percent of MN, 10 to 80 mole percent of TiN, 10 to 90 mole percent of ZrN, and having the mole ratio of AlN to TiN less than 1.2 can be used to make resistive films having a wide range of resistivities, such as from 350 to 10,000 #Qcrn, and having a temperature coefficient of 200 to +150 ppm/C, by using the cathode in an r-f sputtering process.

It has also been discovered that a composite cathode consisting essentially of 10 to 40 mole percent of AIN, 40 to '70 mole percent of TiN and 20 to 50 mole percent of ZrN can be used to make resistive films with a very small temperature coefficient, such as from +125 to l25 ppm/C, and having resistivities in a range of 350 to 1,000 uQcm, by using said cathode in an r-f sputtering process.

Such a composite cathode consisting essentially of TiN, ZrN and AIN can also be used to make resistive films according to the present invention by using the cathode in any other available method of cathodic disintegration, such as an ion beam deposition process as described hereinbefore.

The electrical stability of the resistance of the resistive films according to the present invention is found to be better than 0.1 percent after 1,000 hours in a test at C with no load, which is the same order of stability as that for TiN films. The noise level depends somewhat on the film composition. The typical values observed are -20 to -30 db with 2 to 3 mW/mm The resistive films according to the present invention can be anodized in an electrolyte consisting of ammonium borate and ethylene glycol with a 4 to 16 A./Volt oxidation rate. By using the anodizing process, the present resistive films, like TiN films, can be protected from aging, and at the same time can be trimmed accurately. These facts suggest that the present novel resistive film materials have a high potential not only for use in manufacturing precise thin film resistors in a wide range of resistivities and having high electrical stability, but in the manufacturing of hybrid circuit elements for microelectronics.

It is thought that the invention and its advantages will be understood from the foregoing description.

What is claimed is:

l. A resistive film consisting essentially of AlN, TiN and ZrN, wherein the concentration of said AIN is from 10 to 50 mole percent, the concentration of said TiN is from 10 to 80 mole percent, the concentration of said ZrN is from 10 to mole percent, and the mole ratio of said AlN to said TiN is less than 1.2.

2. A resistive film as claimed in claim 1 in which the concentration of said AIN is from 10 to 40 molepercent, the concentration of said TiN is from 40 to 70 mole percent and the concentration of said ZrN is from 20 to 50 mole percent. 

2. A resistive film as claimed in claim 1 in which the concentration of said AlN is from 10 to 40 mole percent, the concentration of said TiN is from 40 to 70 mole percent and the concentration of said ZrN is from 20 to 50 mole percent. 